This application claims the priority of German patent application 197 41 859.7, filed Sep. 23, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a can comprising a sleeve in the form of a tube made of a plurality of paper layers and two end walls which are inserted into the sleeve and are bonded and sealed thereto. The invention relates furthermore to an arrangement for manufacturing a can of the above mentioned type, comprising a work station for feeding a tube, work stations for inserting at least one end wall in each tube, work stations for bending the tube against the respective inserted end wall and work stations for manufacturing heat seal seams which bond the end wall(s) to the tube.
Cans of this generic type are disclosed in the U.S. Pat. No. 4,286,745. In such cans, the paper layers of the tube forming the sleeve are each bonded by means of an intermediate layer made from a suitable material, such as plastic. The sleeve thus obtains a high stability and flexural strength. Due to the high flexural strength of the can, however, it is difficult to form the tube to establish a bond with the end walls. Therefore, in order to create the bond, the edge areas of the end walls are formed rather than the tube. One the other hand, the material of the end walls should not be too thin, as this unacceptably diminishes the clamping effect of the end walls on the bonding point.
In order to produce this type of can, a tube comprising a plurality of paper layers is rolled at a first arrangement, which tube later forms the sleeve of the can. This tube can be produced by means of winding sheets of paper parallel or helically. The finished tube is fed to another arrangement, where the can is completed of inserting the end walls.
An arrangement of the latter type, on which the present invention is based, is disclosed in U.S. Pat. No. 2,200,276. The arrangement comprises a plurality of sequential work stations, to each of which the paper tube is fed in succession. At the work stations, the end walls are gradually inserted into the tube, which is bent around the end walls and bonded therewith by heat sealing. A work station for heating up the tube is arranged directly upstream of the work station which bonds the compoments. In the work station which heats, hot air is suppled to the end areas of the tube, in which the end walls are already inserted. The hot air streams against the outer side of the tube as well as against its inner side, whereby, due to the already inserted end walls, the hot air reaches only a small way into the inside of the tube. This arrangement takes up much floor space and is very complicated in design.
U.S. Pat. No. 5,135,462 discloses an arrangement for manufacturing a can comprising a paper sleeve and two end walls. A single-layer paper tube is wound from one blank, both end walls are inserted therein and bonded thereto with this arrangement by heat sealing. However, it is not possible to produce a relatively bend-resistant tube, particularly a multi-layered tube made from paper.
It is an object of the present invention to make a can in which the sleeve and the end walls are bonded together in a stable condition. A further object of the invention is to design an arrangement for manufacturing such a can.
This object has been achieved in accordance with the present invention, in which the end walls each comprise a rim projecting outwards, around which rim the tube is bent and bonded by heat sealing. In this manner, it is possible to create a stable and sealed bond between the tube which forms the sleeve and the end walls, without being tied to a certain thickness or rigidity of the material of the end walls.
The rim is already present before the tube is bent around it. Such bending and heat sealing, assure that the end wall is clamped securely and held stable by the relatively thick and bend-resistant tube. The clamping effect is permanently ensured by means of the heat sealing, and the joined point is sealed off additionally.
The end wall has absolutely no supporting function. Material can be used, therefore, which is independent of the supporting function, thus permitting end walls of stronger or weaker rigidity, or greater or less thickness. The material properties of the end walls need only be such that they permit the tube to form a stable and sealed bond.
The relatively thick and bend-resistant material does not prevent the production of a stable and sealed bond. Any problems resulting from the thickness or bend-resistance can be solved by means of a suitable arrangement, further described below.
In an advantageous embodiment of the present invention, the tube forms a heat seal seam on each side of a rim, thus creating a particularly stable and sealed bond between the sleeve and the relevant end wall.
It is also advantageous that the end wall comprises in the area of the rim (on at least one side) a heat sealable plastic layer, thus creating the conditions for a particularly effective stable bond.
In a further advantageous embodiment of the invention, a heat sealable plastic layer is provided on the inside of the tube. A plastic layer of this type can be used for producing the above mentioned heat seal seams as well as for sealing the entire inner surface of the sleeve.
In an advantageous embodiment of the present invention, the end wall consists of paper. This cheap material is very suitable for manufacturing the can of the present invention. As the end wall is supported only by the section of the tube bent around the rim, very little is required of the material of the end wall.
In another advantageous embodiment of the present invention, outside of the area of the rim, the end wall is at least approximately planar.
In still another advantageous embodiment of the present invention, the end wall comprises a filling opening.
The object of the present invention has been achieved in that at least one work station for heating the tube is arranged upstream of the work station for inserting a end wall. Both ends of the paper tube can be heated, so that even the thickest material can be bent and sealed without difficulty. As the heating up takes place before the end walls are inserted, the area of the tube which is covered by the rim of a end wall after it has been inserted can be sufficiently heated. This is vital for forming a sufficiently stable heat seal seam between the rim and the inner side of the tube. In addition, the heat also softens the area of the paper tube to be bent, so that it can bend without difficulty.
In an advantageous embodiment, the working stations for heating the tube are designed so that each inner side of an end area of the tube is heated. In this manner, the plastic layer which is usually applied to the inside of the tube and which plastic layer is used for the heat seal seam, can be directly acted upon.
In a further advantageous embodiment of the present invention the work stations for heating the tube are designed so that the respective outer side of an end area of the tube is heated. Thus the paper layers in particular can be softened for bending.
In yet another advantageous embodiment of the present invention, the work stations for heating the tube include at least one device for feeding hot air to the tube. This permits, by means of simple design, the preparation of the end areas of the tube for bending and sealing.
In still another advantageous embodiment of the present invention, work stations for heating the tube, for inserting a end wall, for bending the tube and for producing a heat seal seam are arranged along the circumference of a first and second star wheels. The star wheels comprise holding devices for a gradually completed can, permitting a simple and compact design of the star wheel.
Advantageously a work station for feeding a tube is arranged the first star wheel.
In another advantageous embodiment of the present invention, the arrangement comprises a work station for affixing a closing element to the filling opening.
According to another advantageous feature of the present invention, a work station is provided for moving aside a closing element from the filling opening. This is particularly practical when the can is filled subsequent to its completion.